198 THE CAMBRIAN. Lblll.81. 



that there is at present no evidence whatever on the north shore of Lake 

 Superior of their holding any other place in the geological series. 1 



This view of Dr. Selwyn's was concurred in by Prof. J. D. Whitney, 

 who stated it to be the opinion held by Messrs. Foster and Whitney 

 thirty years previously. 2 



Dr. Irving took exception to the statement made by Dr. Selwyn that 

 there is no evidence whatever of the rocks holding any other place in 

 the geological series than that including the Potsdam and Primordial 

 Silurian, and stated: 



(1) That tho copper-bearing rocks underlie unconformably, and with an immense 

 unconformity, a series of sandstones holding Cambrian fossils. # * * (2) That 

 the copper-bearing strata also underlie un conformably the " eastern sandstone'' of 

 the south shore of the eastern half of Lake Superior. * * * (3) That the time- 

 gap between the copper-bearing series and the Huronian was too long to allow of 

 our classing them together. 3 



The view of Messrs. Selwyn and Whitney was also opposed by Dr. 

 T. S. Hunt, who referred the basal sandstone to a pre-Oambrian group. 4 



In a note on Dr. Selwyn's paper, Prof. N. H. Winchell concurs with 

 him in the sweeping affirmation that there is at present no evidence 

 whatever of their (i. e., the copper-bearing rocks) holding any other place 

 in the geological series than that of the Potsdam or Primordial Silurian. 

 44 I would also add that there is incontestible evidence that they can hold 

 no other? 5 



In opposition to the view of Prof. Winchell, Prof. Chamberlin stated 

 the evidence upon which the pre-Oambrian age of the copper-bearing 

 series of Lake Superior is based. It is (1) the general stratigraphical 

 relation indicated. This he considers to be the weakest of all. (2) 

 Differences in thickness ; (3) differences in constitution ; (4) unconform- 

 ity ; (5) the inherent inconsistency of the view; (6) the dynamic sim- 

 plicity of the view ; (7) the discovery of a like series in the Grand Caiiou 

 of the Colorado. 6 



Shortly after Prof. Cbamberlin's paper, Dr. M. E. Wads worth pub- 

 lished an article on the relations of the Keweenawan series to the East- 

 ern sandstones. His observations differ from those of Dr. Irving and 

 he claims that the Keweenawan series has no existence distinct from or 

 older than the sandstone of Potsdam age. In speaking of his observa- 

 tions he says, w These observations also prove at the birthplace of the 

 Keweenawan series, that formation and the Eastern sandstone were 

 one and the same." 7 



The paper of Dr. Wadsworth was followed shortly after by one of 

 Messrs. Whitney and Wadsworth on the "Azoic system and its pro- 



•Age of the rocks on the northern shore of Lake Superior. Science, vol. 1, 1883, pp. 11, 221. 



2 Geology of Lako Superior. Science, vol. 1, 1883, p. 39. 



3 The copper-hearing rocks of Lake Superior. Science, vol. 1, 1883, pp. 140, 141, 359, 360, 422. 



4 The Geology of Lake Superior. Science, vol. 1, 1883, pp. 218, 219. 

 6 The Lake Superior Rocks. Science, vol. 1, 1883, p. 334. 



6 The copper-hearing series of Lake Superior. Science, vol. 1, 1883, pp. 453-455. 



7 On the relation of the " Keweenawan series " to the Eastern sandstone in the vicinity of Torch 

 Lake, Michigan. Boston Soc. Nat. Hi&t. Proc, vol. 23, 1884, p. 174. 



